Rheological testing of bitumen at low temperatures with 4-mm DSR

Abstract

To measure bitumen low temperature rheological properties, a new test protocol using a dynamic shear rheometer with 4 mm parallel plates (or called 4-mm DSR) has been proposed in the US. In this paper, a series of experiments including different procedures of sample preparation were carried out to evaluate the 4-mm DSR. Comparison was made with the bending beam rheometer (BBR). The results obtained show that the 4-mm DSR can perform rheological tests at very low temperatures (down below -30 °C). With this new geometry, very little amount of sample is required, making it particularly suitable for study of field aging. There are correlations between complex modulus measured by the 4-mm DSR and creep stiffness by BBR, between phase angle and m-value, as well as between the limiting temperatures determined by the two test methods. With BBR data at 60 s loading time, higher correlation coefficients were observed at lower DSR frequencies or at a frequency corresponding to the 60 s loading time. The correlations seem also to be affected negatively by the waxes of bitumen, probably due to large differences in sample sizes that cause different thermal histories in DSR and BBR, making wax crystallization or physical hardening and its effect on rheology very different. In addition, common DSR with 8-mm plates can be applied to certain low temperatures, depending on instrument compliance and binder stiffness.